I was born when American accents were already homogenizing in the second half of the twentieth century and a friend of mine from Wisconsin once sat me down and ran a compare-and-contrast on our dialects just for the fun of it. I shouldn't be able to be confused by a plane full of characters all from different states.
I think this is something they forgot to do/consider in MotA? I was rewatching a few episodes of BoB and the distinction in accents and intonation between each character was incredible. Not one person sounded the same. They also made sure to cast people with different body types and, with the exception of a few of the younger actors, no one looked alike.